1. Field of the Invention
The present invention relates to a work vehicle in which, on left and right sides of an input case, axle cases are respectively positioned to drive left and right wheels, the input case forming an enclosed space into which an input shaft for engine power transmission is introduced, the axle cases forming enclosed spaces (separate from the previous enclosed space) in which hydraulic continuously variable transmissions are respectively internally installed and supporting axles of left and right traveling wheels, and the left and right wheels being driven via the hydraulic continuously variable transmissions.
2. Description of Related Art
As a work vehicle provided with an input case and axle cases as described above, technologies described in the following [1] and [2] are known.
[1] A work vehicle is known having a configuration in which a base housing into which an input shaft for engine power transmission is introduced and a pump case in which a hydraulic pump body of a hydraulic continuously variable transmission is internally installed are provided, a driving force of the input shaft is transmitted via a first and a second pump shafts to the hydraulic pump body, and a driving wheel is driven via a hydraulic motor body that is fluid-connected to the hydraulic pump body (for example, see Related Art 1).
[2] A work vehicle is known having a configuration in which an input case into which an input shaft for engine power transmission is introduced and an axle case in which a hydraulic continuously variable transmission is internally installed are provided, a driving force of the input shaft is transmitted via a traveling counter shaft to the hydraulic continuously variable transmission, and a rear wheel supported on the axle case is driven by the driving force of the hydraulic continuously variable transmission (for example, see Related Art 2).
[Related Art 1] Japanese Patent Laid-Open Publication No. 2006-64012 (see paragraphs [0021] and [0024], and FIGS. 1, 2, 3 and 7).
[Related Art 2] Japanese Patent Laid-Open Publication No. 2007-196861 (see paragraphs [0024], [0034], [0038], [0042] and [0046], and FIGS. 5, 6 and 8).
In the work vehicle having the conventional structure described in the above [1], the pump case in which the hydraulic pump body of the hydraulic continuously variable transmission is internally installed and the motor unit in which the hydraulic motor body is internally installed are configured using separate cases and are separately supported on a vehicle frame, and the driving wheels are also supported on respective vehicle frame side. Therefore, as a whole, there is a tendency of becoming large in size. Further, the base housing into which the input shaft is introduced, the pump case in which the hydraulic pump body is internally installed, and the motor unit in which the hydraulic motor body is internally installed are configured with separate cases. Therefore, spaces inside these cases are communicatingly connected via a hydraulic circuit by external piping and the like connecting the spaces to each other. Therefore, as the sealing capability required for each of the cases, the sealing capability in common with the case that requires the highest sealing accuracy is required for all the cases. Further, hydraulic oil that passes through the hydraulic continuously variable transmission and lubrication oil that passes through a gear mechanism in the base housing are reservoired in a common reservoir space in the base housing. Therefore, there is a possibility that metal abrasion powder and the like that exist in the reservoir space are sucked in by a fuel pump.
In the work vehicle having the conventional structure described in the above [2], the rear wheels are supported by the respective axle case. Therefore, by supporting the rear wheels by the respective axle case in which the hydraulic continuously variable transmission is internally installed, it is useful in that structural simplification and downsizing can be achieved. However, even in this conventional structure, although the input case into which the input shaft is introduced and the axle case in which the hydraulic continuously variable transmission is internally installed are provided, the space inside the input case into which the input shaft is introduced and the space in which the hydraulic continuously variable transmission is arranged are communicatingly connected by a hydraulic circuit by external piping and the like connecting the spaces to each other. For this reason, sealing capabilities that are set in various ways for each of the cases when a separate oil passage is provided for each of the cases have become common for all oil passages of the cases. Therefore, it becomes necessary to apply the sealing capability in common with the case that requires the highest sealing accuracy to all the cases, and thus, there is room for improvement in this respect. Further, hydraulic oil that passes through the hydraulic continuously variable transmission and lubrication oil that passes through a gear mechanism in the input case are reservoired in a common reservoir space at the bottom of the input case. Therefore, there is a possibility that foreign substances such as metal abrasion powder and the like that exist in the reservoir space are sucked in by a fuel pump. When the shape of the input case is devised to avoid this, the shape of the input case may become complicated, which may lead to circumstances such that maintenance work and the like may become cumbersome.